The present invention relates to improvements in spacers which are used between the marginal portions of panes in multiple-pane windows or the like. The invention also relates to improvements in methods of and apparatus for making such spacers. More particularly, the invention relates to a method of and to an apparatus for converting normally straight tubular blanks into spacers with one or more bends (hereinafter called elbows) each of which is flanked by two normally straight sections of the deformed tubular blank. Such spacers are used between the panes of multiple-pane windows to prevent the penetration of moisture and/or solid contaminants into the space between the neighboring panes as well as to absorb moisture which happens to penetrate into or which has remained in such space. To this end, the spacers contain supplies of a desiccant and are provided with perforations or other types of holes which allow for communication between the interior of the spacer and the space between the major portions of the panes. As a rule, the elbow is a 90-degree bend so that the straight sections of the spacer can remain close to the marginal portions of the panes in a multiple-pane structure having a rectangular or square outline.
U.S. Pat. No. 4,261,145 to Brocking discloses spacers for multiple-pane windows as well as a method of and an apparatus for making the spacers. The blanks are elongated tubular bodies which are filled with desiccant and are bent in such a way that the ends of the resulting spacers are remote from the corners of the panes in order to facilitate coupling of the ends of a single spacer or of the ends of two or more discrete spacers to each other in order to form a circumferentially complete spacer which extends along all marginal portions of the respective pair of panes. Even though the patent to Brocking also refers to the making of miter joints at the corners of neighboring panes, it discloses the making of butt joints in regions other than the corners of a multiple-pane window. There is also disclosed the possibility of bending an elongated tubular blank at four spaced locations so as to obtain a one-piece spacer whose ends are joined by a suitable coupling insert to thus obtain a circumferentially complete distancing device extending along all four marginal portions of the neighboring panes. A drawback of the patented proposal is that the walls of the tubular blank are likely to burst or break in response to pronounced bending, especially in view of the fact that the blank is filled with a desiccant which resists bending of the adjoining walls of the blank in order to form a 90-degree elbow. Therefore, the patentee proposes to evacuate a certain amount of desiccant by vibrating the tubular blank. This contributes to complexity of the apparatus and necessitates the provision of means for intercepting the escaping desiccant for renewed use. Moreover, evacuation of a certain amount of desiccant from the regions where the blank is to be formed with elbows fails to invariably prevent cracking or bursting of the bent portions of a blank because some of the material of the blank must expand and some material must contract during the making of one or more elbows. Cracking of the blank during the making of one or more elbows results in the establishment of communication between the compartment for desiccant and the surrounding atmosphere so that the desiccant is rapidly saturated and is incapable of withdrawing moisture from the space between the neighboring panes. The result is rapid clouding or fogging of the multiple-pane window. The problem is aggravated due to the fact that, as a rule, the manufacturer wishes to make elbows with small or very small radii of curvature in order to ensure that each elbow will extend close to the respective corners of the neighboring panes. This ensures that the elbow is less likely to be visible, or is not visible at all, in the fully assembled multiple-window pane. The making of such elbows with minute radii of curvature renders it even more likely that the entrapped desiccant will cause the material of the spacer at the outer side of the elbow to break or burst as a result of pronounced elongation during bending of the tubular blank around a mandrel or the like.
German Pat. No. 30 47 338 discloses a modified tubular blank for conversion into spacers which can be used between the marginal portions of panes in multiple-pane windows. In accordance with the proposal which is disclosed in this patent, the blank contains a first longitudinally extending compartment which is filled with a suitable desiccant and a second longitudinally extending compartment which is empty and is outwardly adjacent to the first compartment when the blank is converted into a spacer with one or more elbows. Consequently, the wall at the outer side of the empty compartment undergoes maximum elongation during the making of an elbow whereby the walls bounding the compartment which contains the desiccant are less likely to burst during bending of such blank. The just described blank is quite satisfactory and is much less likely to burst during bending than the blank of Brocking. However, the cost of the twin-compartment blank is much higher and the dimensions of such blank (as considered at right angles to the longitudinal direction of the blank) are greater so that the spacer cannot be readily concealed in the fully assembled multiple-pane window.
In accordance with a further proposal, bending of a tubular desiccant-filled blank is facilitated by weakening that wall of the blank which is located at the inner side of the elbow in a completed spacer. The weakening is effected by removing some material to form in the inner wall grooves, blockouts and analogous formations which render the respective wall more readily pliable and thus reduce the overall resistance of the blank to bending. The weakened portions have perforations which establish communication between the interior of the spacer and the space between the respective panes. Since the desiccant invariably undergoes a pronounced grinding or other comminuting action while a straight piece of tubular blank is being converted into an elbow, the comminuted desiccant penetrates from the interior of the elbow into the space between the panes when the multiple-pane window is fully assembled. This detracts from the appearance of the finished product. In fact, and since the panes in a finished window invariably have some freedom of movement relative to one another, e.g., in response to changes in temperature, these panes act not unlike a suction pump whenever they move apart to thereby draw additional desiccant from the holes at the inner side of an elbow. Such pumping action can entail migration of relatively large quantities of comminuted desiccant from the interior of the elbow into the space between the neighboring panes.